This invention relates to a decanter centrifuge comprising an axially symmetrical bowl and a conveyor screw journalled therein.
Such a decanter centrifuge is employed for separating a slurry supplied to the interior of the bowl into a solids phase and one or more liquid phases. This is obtained by rotating the entire centrifuge at a high number of revolutions and rotating at the same time the conveyor at a low number of revolutions relative to the bowl.
The separating effect of the centrifuge and its capacity or throughput depend, on one hand, on the magnitude of the field of gravitation generated by the centrifugal force in the separating space of the bowl, i.e. on the number of revolutions and the inner diameter of the bowl and, on the other hand, on the length of the separating space.
A factor of decisive importance for the maximum allowable number of revolutions is the flexural rigidity of the conveyor radially supported at both ends of the bowl because the flexural rigidity determines the critical number of revolutions of the conveyor.
This fact has hitherto implied that the .lambda.-value of a given centrifuge--the .lambda.-value being defined as the ratio between the length and the inner diameter of the separating space--has not in practice exceeded values of about 5.
In cases where a large field of gravitation and a large capacity have been required, the resulting centrifuges have been excessively large and expensive. This relates to the fact that a straight geometrically enlargement of a given decanter centrifuge has caused the costs of manufacture to increase by the cube of the scale ratio, while the capacity only increases by the square of the scale ratio.
In view of the fact that, inversely, a capacity increase proportional to the extension is obtained simply by increasing the length of the centrifuge--without a corresponding rise in price--it is obvious to aim at producing decanters having .lambda.-values exceeding said approx. 5.